In connection with the employment of vestibule-valve refill arrangement (see U.S. patent application Ser. No. 627,803 filed on Oct. 31, 1975, now U.S. Pat. No. 4,029,473), it was discovered that commercially available pressure regulators of sufficient sensitivity and adequate control accuracy to refill a remote vestibule vessel to a desired level were very expensive. Furthermore, none available were at all suitable for reliable operation with a system required to handle reagents and solvents of corrosive and otherwise agressive characteristics.
The present invention is designed to circumvent the problem of expensive pressure regulators by measuring and controlling the liquid head in the supply vessel so as to thereby control the liquid fill level in a remote "vestibule vessel."
It is a further object of the present invention to accomplish the desired control with relatively inexpensive commercially available photoelectric detectors, solenoid valves, sample fittings and parts readily fabricated from materials, such as glass, which is appropriate for the liquids to be handled.
It is a further object to provide a closed liquid delivery system in which the reagents are protected from exposure to the atmosphere and in which the operating gas may be dry nitrogen or other inert dry gas.
Another object of the invention is to provide a system which is "fail-safe" against accidental overpressure or accidental failure of certain components such as incandescent lamps in the liquid detector devices.
More particularly, in systems according to the invention the liquid head at the reservoir vessel is monitored directly and conveniently with relatively simple inexpensive available equipment. Also, a malfunction detector and associated alarm is also readily provided for simply detecting "over-pressure" and "over-flow" conditions to responsively invoke an automatic alarm and "shut-down," as well as to vent the pneumatic drive system. The resulting system is relatively insensitive to rather wide variations in required driving gas pressure, requiring no special adjustments for various densities of transferred liquids, and is relatively insensitive to variations in ambient and supply pressure. Also, it will continue to supply reagent to a transfer vessel despite a relatively massive gas leakage from the system. Also, according to other features of the invention, such systems provide an immediate, and direct, indication of significant gas leakage from the system (e.g. from a supply vessel closure or from any of the gas delivery lines and associated seals).
Thus, it is an object of the present invention to provide at least some of the foregoing solutions and features of advantage in an improved liquid dispensing system. A related object is to provide such an improved system wherein liquid is transferred from a reservoir to a transfer vessel by pneumatic means operated automatically according to controls monitoring a liquid level directly related to the liquid level in this vessel. A related object is to provide such a system wherein automatic drive-pressure control is achieved via direct detection of this liquid level, rather than indirectly, such as by monitoring pressure.
A related object is to provide such a system using inexpensive, readily available liquid level detector means. Yet a further object is to provide such using an array of photosensor means adapted to detect the rising level of liquid in a riser tube communicating with a reservoir and wherein control means responsive to detected high liquid levels are adapted to vent the pneumatic drive-system in a controlled pulsed fashion.
Yet a further object is to provide such a system wherein an "over-flow" detect means is supplementarily provided and is adapted to detect extreme, "over-flow" levels of stored liquid and responsively relieve the pneumatic replenishment system in a "fail-safe" manner. A further object is to provide such a system and detector adapted to vent the supply reservoir and to disable all fill-operations until "reset."
These and other objects of the invention will become more apparent from the following description and appended claims, reference being made to the accompanying drawings forming a part of the specification.